Plenty of information buried on this forum. Do lots of reading. Study the geography of the lines on Google Maps. Use the working timetables if you need very specific timings. Know that attempt #1 won't go to plan and improvisation skills improve with time.

I know it's an odd station but the parking is cheaper than Heathrow and its a long walk from terminal 5 to the long stay car park. I know there is a shuttle bus but I can't find what happens with that overnight

You don't need to start your stopwatch on the first train you take of the day, just when you want to start the attempt. So, assuming you're doing Heathrow to begin with, you don't need to start your stopwatch until you depart Terminal 4, since you'll be going back through Hatton Cross anyway.

You don't need to start your stopwatch on the first train you take of the day, just when you want to start the attempt. So, assuming you're doing Heathrow to begin with, you don't need to start your stopwatch until you depart Terminal 4, since you'll be going back through Hatton Cross anyway.

Which is what I was hinting at above without completely giving the game away...

You don't need to start your stopwatch on the first train you take of the day, just when you want to start the attempt. So, assuming you're doing Heathrow to begin with, you don't need to start your stopwatch until you depart Terminal 4, since you'll be going back through Hatton Cross anyway.

Which is what I was hinting at above without completely giving the game away...